As a consequence of the standardization for current CPU or inner structural parts, it is getting more difficult to make a difference in electronic equipments such as personal computers, digital cameras, digital video cameras, cell phones and the like. In order to distinguish the electronic equipment from other electronic equipments available in the market, it is necessary to improve decorativeness, such as color tone, gloss and the like, with respect to the external appearance of the housing of the electronic equipment.
To provide housings for electronic equipments with improved portability, a highly rigid plastic formed by adding carbon fibers (CF) or glass fibers (GF) to polycarbonate (PC) resin or polyamide (PA) resin, a material formed by immersing carbon fibers (CF) in thermosetting plastic, and the like are used. To provide housings for electronic equipments with improved decorativeness, a metallic multi-layered coating added with alumina powder, and a piano-gloss coating by applying a clear coating have been applied. It is expected that there will be more demands for the housings for electronic equipments to have patterns, characters, or pictures printed thereon in the future.
It has been known that the housing formed of Mg alloy tends to cause molding failures such as sink mark, void, flow line (seam) and the like at high rate. These molding failures (sink mark, void, flow line (seam) etc.) lead to failures of the external appearance even after coating. Therefore, it is necessary to process the Mg alloy housing by manually coating putty, or applying a UV coating, to compensate these molding failures before the coating is applied, and this leads to the increase in cost. Namely, the Mg alloy housing has problems such as difficulties in molding, low mass-productivity, requiring smoothing treatment of the surface after molding, and the like.
Moreover, the spray coating which is applied for improving the decorativeness of the housing requires an undercoat (primer) and overcoat, and thus it tends to cause the failures of the external appearance due to the contamination of foreign substances other than the materials to be used, and to lower production yield. Especially with the gloss coating for imparting metallic appearance, as the coating needs to be applied a few times, the production yield tends to be lowered because of the contamination of dust or waste.
As mentioned above, there are many problems in improving both the production yield and decorativeness of the housing of an electronic equipment. For example, it is difficult to provide the Mg alloy housing with excellent decorativeness at low cost. Moreover, the problems associated with the decorativeness are caused likewise in the case of metal housings of Al or Ti, or plastic housings, other than that of Mg alloy (see Japanese Patent Application Laid-Open (JP-A) No. 2003-160898 and Japanese Patent (JP-B) No. 3641233).